1. Field of the Invention
The present invention relates to an electromagnetic coil assembly for use in an electromagnetic apparatus, such as an electromagnetic clutch for use in controlling the transmission of power from an automobile engine to a refrigerant compressor in an automobile air conditioning system. More particularly, it relates to the structure for a securing member, which secures a thermal protection device in the electromagnetic coil assembly.
2. Description of Related Art
Referring to FIGS. 1 and 2, an electromagnetic coil assembly 4, which comprises a bobbin 1 and a coil 3, is known in the art. Bobbin 1 has a toroidal shape having a spool portion, which has an exterior open edge. Coil 3 is formed of an electrical wire 2, which is wound around the spool portion. An electromagnetic coil assembly 4, for example, is used in an electromagnetic clutch 6 of a compressor 5 in an automobile air conditioning system, as shown in FIG. 3. Electromagnetic coil assembly 4 may be provided with a thermal protection device 7, eg., a thermal fuse or a thermal switch, which is sensitive to high temperatures in electromagnetic clutch 6. Thermal protection device 7 isolates a power source, such as an automobile engine, to protect electromagnetic clutch 6 and compressor 5 when high temperatures due to friction between the parts in electromagnetic clutch 6 are generated.
Referring again to FIGS. 1 and 2, in electromagnetic coil assembly 4, thermal protection device 7 has a pair of leads, a first lead 7a and a second lead 7b, extending from either end of thermal protection device 7. An end of first lead 7a of thermal protection device 7 is connected to a wire end portion 2a of electrical wire 2 through a first caulking terminal 8. An end of second lead 7b of thermal protection device 7 is connected to a third lead 9, which is connected to the external power source (not shown), through a second caulking terminal 10. Thermal protection device 7, first lead 7a and second lead 7b, wire end portion 2a, and a beginning portion of third lead 9 are disposed on a first end surface 1a of bobbin 1. A pair of projection portions, a first projection portion 12a and a second projection portion 12b, are formed on first end surface 1a. Moreover, a securing member 11 having a groove-shaped cross-section, which is integrally molded with bobbin 1, is disposed on a first end surface la of bobbin 1. Securing member 11 extends on first end surface 1a and crosses at a right angle to the radial axis of the spool portion of bobbin 1. An open edge of a groove of securing member 11 formed opposite to first end surface 1a. 
When thermal protection device 7, first caulking terminal 8, and second caulking terminal 10 are disposed on first end surface 1a of bobbin 1; a wire portion, which consists of wire end portion 2a of electrical wire 2 through beginning portion of third lead 9, is drawn along the circumference of first end surface 1a. First lead 7a of thermal protection device 7 is secured by first projection portion 12a from the exterior open edge of bobbin 1. Thereafter, thermal protection device 7 is inserted into the groove of securing member 11, and second lead 7b of thermal protection device 7 is secured by second projection portion 12b from the exterior open edge of bobbin 1. Thus, thermal protection device 7, first caulking terminal 8, and second caulking terminal 10 are secured on first end surface 1a of bobbin 1.
As shown in FIG. 4, in electromagnetic coil assembly 4, the groove of securing member 11 is formed of a first side wall 11a, which is positioned radially outward on first end surface 1a, and a second side wall 11b, which is positioned radially inward on first end surface 1a. A height of first side wall 11a is the same as a height of second side wall 11b. Therefore, thermal protection device 7 is inserted into the groove of securing member 11 from a direction perpendicular to the groove, as shown in the arrow of FIG. 4.
With respect to securing thermal protection device 7, the insertion of thermal protection device 7 into the groove of securing member 11 from the perpendicular direction may not be done in a series of steps, which consist of drawing the wire portion along the circumference of first end surface 1a, and securing first lead 7a and second lead 7b by projection portion 12a and projection portion 12b. When thermal protection device 7 is inserted into securing member 11 from a direction above and perpendicular to the groove of securing member 11, the steps of drawing the wire portion along the circumference of first end surface 1a may be interrupted. As a result, the efficiency of the process of securing thermal protection device 7, first caulking terminal 8, and a second caulking terminal 10 on first end surface of bobbin 1 may be reduced.
A need has arisen to provide an electromagnet assembly for use in an electromagnetic apparatus which has an improved efficiency in fixing a thermal protection device and caulking terminals to an end surface of a coil bobbin, when compared with a known electromagnet assembly.
In an embodiment of the present invention, an electromagnetic coil assembly for an electromagnetic apparatus comprises a bobbin, a coil, and a thermal protection device. The bobbin comprises a cylindrical tubular spool, and a pair of annular flanges projecting radially from the spool to form an exterior open edge. The coil is formed of an electrical wire. The electrical wire is wound around the spool between the flanges. The thermal protection device has a first and a second lead wire, each extending from one side thereof. The first lead wire is connected to one end of the electrical wire through a first connecting member. The second lead wire is connected to one end of a third lead wire of an electrical circuit through a second connecting member. The thermal protection device, the first lead wire, the second lead wire, the first connecting member, the second connecting member, one end of the electrical wire, and one end of the third lead wire are disposed on a first end surface of the bobbin. A securing member having a groove-shaped cross-section is securely disposed on the first end surface of the bobbin. The securing member extends on the first end surface and crosses at a right angle to a radial axis of the spool, such that the thermal protection device is inserted into a groove of the securing member. A height of a fist side wall of the securing member, which is positioned radially outward on the first end surface, is lower than a height of a second side wall of the securing member, which is radially inward on the first end surface.
Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following description of the invention with reference to the accompanying drawings.